The physiological and biochemical significance of glutamine utilization is being studied in the intestinal epithelium using in vitro preparations of isolated epithelial cells, everted sacs, slices, and organ cultures. Guinea pig enterocytes were examined using as criteria of viability the maintenance or Na/K gradients, energy charge, oxidative processes, glycolsis, de novo purine synthesis protein synthesis, uridine or uracil incorporation to RNA, thymidine incorporation to DNA, and capacity to accumulate transported metabolites. Using specific enzyme inhibitors the importance of certain enzymes in the pathways of glutamine oxidation is being studied. Glutamine synthetase has been found in the intestinal mucosa and is being characterized.